With each successive semiconductor technology generation, wafer diameters tend to increase and transistor sizes decrease, resulting in the need for an ever higher degree of accuracy and repeatability in wafer processes. Semiconductor substrate materials, such as silicon wafers, are processed by techniques which include the use of vacuum chambers. These techniques include non plasma applications such as sputter deposition, as well as plasma applications, such as plasma-enhanced chemical vapor deposition (PECVD), resist strip, and plasma etch.
Plasma processing systems available today are subject to a number of specific modes of failure. Many such modes are difficult to detect prior to processing an actual device wafer, and can result in the misprocessing of the wafer. While detection systems exist to diagnose certain aspects of the plasma such as the ion density or the electric field, insufficient methods are available for the detection of faults. Among other things, this calls for plasma chambers with improved uniformity, consistency and self diagnostics. Improved plasma sensing technology which facilitates the achievement of these goals is in great demand.